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Abstract

Background: Although proteomics has been previously applied to vascular tissues, none of these studies has specifically targeted the vascular extracellular environment.

Methods and Results: We developed a novel biochemical fractionation methodology in human aortas that enabled us to identify 103 extracellular proteins by nanospray liquid chromatography tandem mass spectrometry, of which one third have never been reported in the proteomics literature of vascular tissues so far. In particular, three glycoproteins (podocan, sclerostin, and agrin) were identified for the first time in human aortas at the protein level. We also identified AEBP1, a mediator of foam cell formation, the cartilage glycoprotein asporin and a previously hypothetical protein, RPE-spondin. We next applied this proteomic method to further our understanding of extracellular matrix remodelling and degradation in human abdominal aortic aneurysm (AAA). A proteomic comparison between control aortas and AAA revealed that the presence of MMP-12 was associated with extensive degradation of matrix glycoproteins, such as tenascin, collagen type XII, thrombospondin-2, periostin and AEBP-1, which were not previously known to be substrates of MMP−12. By incubating control aortic tissue with recombinant MMP-12, we were able to relate the degradation of these glycoproteins to MMP-12 activity in the AAA extracts. Moreover, proteomics revealed the accumulation of podocan, originally described as a glycoprotein secreted by kidney podocytes. The increased expression of this novel glycoprotein in AAA was confirmed by immunohistochemistry. In functional experiments, podocan emerged as a potent inhibitor of aortic smooth muscle cell proliferation and migration.

Conclusion: In conclusion, our innovative proteomics approach enabled us to provide the most detailed characterization of extracellular matrix components in human aortas to date and explore their degradation in AAA. This comparison revealed a distinct role of MMP-12 in extracellular matrix remodelling and identified podocan as a novel inhibitor of smooth muscle cell migration demonstrating the potential of state-of-the-art proteomics for clinical applications.